Many devices that employ magnetic fields have heretofore been encumbered by massive solenoids with their equally bulky power supplies. Thus, there has been increasing interest in the application of permanent-magnet structures for such uses as electron-beam focusing and biasing fields. The current demand for compact, strong, static magnetic field sources that require no electric power supplies has created needs for permanent magnet structures of unusual form. A number of configurations have been designed and developed for electron-beam guidance in mm/microwave tubes of various types; for dc biasing fields in millimeter wave filters, circulators, isolators, strip-lines; for field sources in NMR (nuclear magnetic resonance) imagers; and so on.
Various prior art structures have contributed to the development of technology in this area. For example, U.S. Pat. No. 3,768,054 to Neugebauer, entitled "Low Flux Leakage Magnetic Construction", teaches a number of magnetic circuits utilizing magnetic cladding means to reduce exterior flux leakage an increase the controlled magnetic field intensity. The advantageous features of this and similar devices are, significantly, the reduction of flux loss and very effective control without any increase, in fact most times a decrease, in the size or weigh&. of the magnetic circuit elements.
In many of the prior art structures magnetic fields emanate from the structure parallel to its axis. These structures have provided remarkable results such as significant reduction of flux loss and effective control and increase of the magnetic field intensity. There has been little work done in providing structures with controlled magnetic fields other than those parallel to the axis of the structure.